Sealing device for rotating shaft

ABSTRACT

When the annular seal 11 which provides sealing around a shaft 1 is damaged, something which is signalled by an oil leak, the axially mobile seal carrier 10 is pushed to the left, with the aid of the lug 13, to bring an additional seal 12 into service, this making it possible to eliminate the leak without any dismantling. This operation can be brought about by a jack and can be automated. 
     Application to all rotating shafts.

The present invention relates to a sealing device for rotating shaft,intended to prevent leaks of a lubricant medium at a bearing supportingthe shaft of a machine, this device including, for this purpose, betweenstationary parts and rotating parts of the machine, a seal carriermounted in sealed manner on a stationary part, this seal carriercarrying at least one first annular seal surrounding the shaft andprovided with a flexible sealing lip capable of providing sealed contactwith a rotating bearing surface integral with said shaft.

When an oil leak or leak of some other lubricant medium is detected insuch a device, it is necessary to dismantle certain components,especially the seal carrier, in order to replace the defective seal witha new seal. In general, in effect, leaks result from wear or some otherdamage of the lip of the annular seal, irrespective of the care withwhich the rotating bearing surface of the shaft is made; the leak israrely the result of deterioration of this bearing surface.Nevertheless, changing a seal still represents an operation which takestime and requires the machine equipped with the shaft in question to beimmobilized for some length of time, which may represent a considerabledrawback, aside from the increase in the cost of maintaining themachine.

The object of the present invention is to avoid these drawbacks, and tothis end, a sealing device of the type defined at the beginning ischaracterized in that said seal carrier is mounted so that it can moveaxially on said stationary part and carries at least one additionalannular seal of the aforementioned type, the first seal being in rubbingcontact with said bearing surface, while the additional seal or sealsare normally not in contact with this bearing surface, it being possiblefor a given-amplitude axial shift of said mobile seal carrier to bringsaid first seal out of contact with said bearing surface and bring thenext first additional seal into contact with this bearing surface.

Thus, as soon as a leak is detected, all that will be required will beto shift said mobile seal carrier axially in order to bring the firstseal, assumed to be responsible for the leakage, out of service andbring the second seal (or the other additional seals in succession) intoservice, something that will not require any dismantling and in any casewill require the use only of very simple and quick operations, thesaving of time by comparison with that required for dismantling the sealcarrier being considerable.

To avoid contact with the worn seal previously in service, as well aswith the additional seal following the one which is in service, whichwould cause needless friction, the device of the invention may furtherbe characterized in that said rotating bearing surface of the shaft,capable of providing sealed contact with the lip of at least one of theannular seals, has axially, on each side of a bearing surface proper, aradially set back region making it possible to contrive for the lip ofone single seal to be in contact with said bearing surface.

This device may further be characterized in that said axially mobileseal carrier is mounted as a sliding ring in a stationary annular sealcarrier integral with said stationary parts of the machine, sealingbetween the stationary seal carrier and mobile seal carrier as well asbetween stationary seal carrier and stationary parts being provided byO-rings, which provides sealing at all levels, between stationary partsand axially mobile parts of the machine.

The mobile seal carrier could be shifted axially and locked in thedesired position by any appropriate means.

The device could thus be further characterized in that said mobile sealcarrier includes at least one lug accessible from the outside andcapable of being locked on a stationary part in at least two axiallyoffset positions, namely a position for which one annular seal providesthe seal between said rotating bearing surface of the shaft, and aposition for which the immediately next additional seal provides thisseal.

It is particularly appropriate to provide that said lug of the mobileseal carrier is arranged so that it can slide in an axial slot of saidstationary annular seal carrier and can be locked in at least the twosaid axially offset positions by a wedge or the like capable of beingslipped through a hole in said lug and of passing at the same time andselectively through two pairs of axially offset stationary lugs of saidstationary seal carrier. This device displays the advantage ofsimplicity and also of providing rotational locking of the mobile sealcarrier which is prevented from turning inside the stationary sealcarrier by its lug, guided by said axial slot.

In another embodiment, it is possible to provide for the use of a screwjack to assume the shifting of the axially mobile seal carrier.

The device could then be characterized in that it includes an annularscrew jack mounted on said stationary annular seal carrier and capableof exerting an axial pressure on said lug of the mobile seal carrier.

This annular jack could, for example, include on the one hand a threadedbushing mounted on said stationary annular seal carrier and preventedfrom rotating with respect to the latter and, on the other hand, anouter ring screwed onto the threaded bushing and capable, by rotating,of exerting an axial thrust on said lug of the mobile seal carrier, acirclip or the like being able to limit the axial displacement of thislug depending on the position in which it is blocked on the stationaryseal carrier.

According to another alternative form, it would be possible to use afluid-pressure annular jack.

In this case, the device could be characterized in that said stationaryannular seal carrier internally has an annular chamber including anannular piston capable via one of its ends of exerting a thrust on saidlug of the mobile seal carrier, it being possible for its other end tobe subjected to the pressure of an actuating fluid, a circlip or thelike being able to limit the axial displacement of this lug depending onthe position in which it is blocked on the stationary seal carrier.

Such a device may then easily be automated and then be characterized inthat it includes means for automatically feeding said annular chamberwith pressurized actuating fluid, these means themselves beingcontrolled from a leak detector.

Embodiments of the invention will now be described by way ofnon-limiting examples with reference to the figures of the attacheddrawing in which:

FIG. 1 represents two half-views in axial section of a sealing devicefor a rotating shaft in accordance with the invention;

FIG. 1a is an external part view of this device, in perspective;

FIG. 2 represents two half-views in axial section of an alternative formwith screw jack;

FIG. 2a is an external part view of the device of FIG. 2, inperspective;

FIG. 3 represents two half-views in axial section of another alternativeform of the device, including a jack with actuating fluid; and

FIG. 3a diagrammatically represents an automatic control for the deviceof FIG. 3.

In all the figures, elements which are identical, similar, or have thesame purpose are denoted by the same references. The rotating shaft hasbeen referenced as 1, and as 2 is a ring wedged on the shaft in terms ofrotation and axially, this ring on its outside having a carefullymachined cylindrical bearing surface 3. The shaft is supported by astationary machine part 4 via rolling-contact bearings 5. The presenceon each side of the bearing surface 3 of radially set back regionsreferenced 6 in FIG. 1 should be noted. Fixed to the stationary part 4of the machine, by screws of axis 7 is a stationary annular seal carrier8 provided with an axial slot 9. On each side of the two ends of thisslot, this seal carrier has pairs of lugs referenced 13a and 14a andpierced with two holes opposite each other (which are visible, but notreferenced).

Mounted in this stationary seal carrier, in such a way that it can slidelike a piston, is an annular and therefore axially mobile seal carrierreferenced 10 in an internal cylindrical cavity of which there are fixedtwo annular seals referenced 11 and 12 respectively, the sealing lips ofwhich are urged radially and inwards by elastic circular snap rings 11aand 12a respectively, all this being in the known way. At its outer end,the mobile seal carrier 10 has a lug 13 pierced with a hole and engagedin the aforementioned axial slot 9. Between the stationary part 4 andthe stationary seal carrier 8 on the one hand, as well as between thestationary seal carrier 8 and the axially mobile seal carrier 10 on theother hand, the seal is provided by two small O-rings which are visiblebut not referenced.

That being so, it can be seen in the upper sectional half-view of FIG. 1that only the first seal 11 provides a seal about the rotating parts,its lip pressing against the bearing surface 3 of the ring 2. The mobileseal carrier 10 is locked in this position by a spindle or pin 15passing through the holes facing each other of the lugs 13 and 13a, thelug 13 moreover preventing the mobile seal carrier 10 from rotating withrespect to the stationary seal carrier 8. When a leak is detected, theleak being due in most cases to wear or damage of the lip of the seal11, all that is required is for the pin 15 to be withdrawn, the lug 13to be slid in the slot 9 into the position for which it comes facing thelugs 14a, then for the assembly to be relocked using the pin 15 nowpassing through the lug 13 and the lugs 14a. In this position, and asvisible in the lower sectional half-view of FIG. 1, the additional seal12 takes over from the worn seal 11, its sealing lip in turn coming intocontact with the bearing surface 3 of the ring 2, while the lip of theseal 11 is brought away from this bearing surface.

Represented diagrammatically and partially at 16 is a tool in the formof two half-shells allowing convenient manipulation of the mobile sealcarrier 10 in the stationary seal carrier 8. Sliding is favoured by thepresence of Teflon-coated bearing surfaces 17 on the mobile sealcarrier.

It should also be noted that in order to limit wear on the bearingsurface 3, notwithstanding the use of two successive seals 11, 12 (or ofa greater number of seals), and if need be to eliminate a leak resultingfrom a defect on the bearing surface 3, the circular region of thissurface 3 which is in contact in succession with the lip of the seal 11then with the lip of the seal 12 or of the other successive additionalseals is offset slightly by an axial distance denoted as e. This measuremay be adopted irrespective of the embodiment: all that is required isto contrive for the axial offset of the mobile seal carrier 10 to bedifferent each time, by the value e, from the axial distance separatingthe lips of two successive annular seals.

In the embodiment of FIG. 2, use is made of a screw jack for exerting athrust on the lugs 13 of the axially mobile seal carrier 10. To thisend, a threaded bushing 18, for example one made of rigid syntheticmaterial wedged in terms of rotation and axially with respect to thestationary seal carrier 8, has been engaged over the stationary sealcarrier 8. To achieve this, tabs 19 at the ends of this bushing engagein oblong holes 20 of the stationary seal carrier. A ring 21 withengagement projections 22 is screwed tight (to prevent untimelyrotation) onto the threaded bushing 18 and may thus, when made to rotate(for example using a tool) exert an axial thrust on at least twodiametrically opposed lugs 13 of the mobile seal carrier 10, withinterposition of a low-friction washer 23. During normal operation, themobile seal carrier 10 can be locked axially by a circlip 24 snap-fittedinto an annular groove 25 of the stationary seal carrier 8, for use ofthe first seal 11, or into another annular groove 26 of the stationaryseal carrier, for use of the additional seal 12 after the previous onehas been taken out of service.

In the embodiment of FIG. 3, the stationary annular seal carrier 8includes an annular chamber 27 in which an annular piston 28 is mountedso that it can slide. A protruding end of this piston bears against thelugs 13 (there being two or three of these distributed at equal angles)of the axially mobile seal carrier 10. The circlip 24 serves the samepurpose as in the previous embodiment.

Screwed onto the stationary seal carrier 8 is a self-closing stopper 29with a ball valve by means of which the chamber 27 may be fed withpressurized actuating fluid, for example using a hand pump. When thefirst seal 11 is worn, all that is required is for the circlip 24 to beremoved and placed in the annular groove 26, and for the pressurizedactuating fluid supply to be connected to the stopper 29 in orderaxially to displace the mobile seal carrier 10, bring the seal 11 out ofservice and bring the additional seal 12 into service, this requiringjust a minimum number of operations, as can be seen.

These operations may moreover easily be automated, for example accordingto the diagram of FIG. 3a: a leak detector 30 situated close to the lipof the seal to be monitored may provide a visible signal, at 31,together with an electrical signal to an amplifier 32. The latter canthen automatically make a solenoid valve 33 situated on the circuit 34for feeding the stopper 29 with pressurized fluid open. On the basis ofthe visual signal 31, an operator can also cause the solenoid valve 33to open by pressing a push button 35. These operations do not requirethe machine to be shut down.

Finally, it should be noted that between the mobile seal carrier 10 andstationary seal carrier 8, the abovedescribed "clear-cut" physical stopsmay, if they have to, be dispensed with, the use of positionalreferences making it possible visually and quickly to observe thesituation of each of the devices equipped in accordance with theinvention.

I claim:
 1. A sealing device for a rotating shaft for preventing leaksof a lubricant medium at a bearing supporting a shaft of a machine, saidsealing device comprising at least one stationary part, a rotatingshaft, and an axially mobile seal carrier mounted between said at leastone stationary part and said rotating shaft in a sealed manner on astationary annular seal carrier, said axially mobile seal carriercomprising at least a first annular seal surrounding said rotating shaftand a flexible sealing lip for providing sealed contact with a rotatingbearing surface integral with said rotating shaft, wherein said axiallymobile seal carrier is mounted for axial movement on said stationaryannular seal carrier and comprises at least one additional annular seal,wherein said first annular seal is in contact with said rotating bearingsurface, while said at least one additional annular seal is not incontact with said rotating bearing surface, and said first annular sealis out of contact with said rotating bearing surface while said at leastone additional annular seal is in contact with said rotating bearingsurface and wherein said axially mobile seal carrier comprises at leastone lug accessible from outside and capable of being locked on saidstationary annular seal carrier in at least two axially offsetpositions, namely a position for which said first annular seal providesa seal between said rotating bearing surface of said rotating shaft, anda position for which an immediately next additional at least one sealprovides said seal.
 2. A device according to claim 1, wherein saidrotating bearing surface of said rotating shaft comprises axially, oneach side of said rotating bearing surface, a radially set back regionfor contriving a lip of one single seal to be in contact both with saidrotating bearing surface, preventing contact with said first annularseal, as well as with said at least one additional seal followinganother at least one additional seal which is in service.
 3. A deviceaccording to claim 1, wherein said axially mobile seal carrier ismounted as a sliding ring in said stationary annular seal carrierintegral with said stationary part of the machine, and wherein sealingbetween said stationary annular seal carrier and said axially mobileseal carrier as well as between said stationary annular seal carrier andsaid at least one stationary part is provided by O-rings.
 4. A deviceaccording to claim 3, wherein said axially mobile seal carriercomprising a lug for sliding in an axial slot of said stationary annularseal carrier and locking in at least two axially offset positions.
 5. Adevice according to claim 4, characterized in that said lug (13) can beshifted manually in said axial slot (9) of the wherein said stationaryannular seal carrier comprises an axially slot and said lug can beshifted manually, in said axial slot and can be locked by a wedgecapable of being slipped through a hole in said lug and of passingsimultaneously and selectively through two pairs of axially offsetstationary lugs of said stationary seal carrier.